A railroad network normally contains one or more switchyards in which cars are routed from tracks leading from a departure point to tracks going to a destination point. A typical switchyard has four main components, namely receiving tracks, a car switching mechanism, a set of classification tracks and a set of departure tracks. Incoming trains deliver cars in the receiving tracks. The cars are processed by the switching mechanism that routes individual cars to respective classification tracks.
Two types of switching mechanisms are in use today. The first one is a hump switch. Switchyards that use a hump switch are referred to as hump yards. A hump switchyard uses a hump over which a car is pushed by a locomotive. At the top of the hump the car is allowed to roll on the other side of the hump under the effect of gravity. Retarders keep the car from reaching excessive speeds. The hump tracks on which the car rolls down the hump connect with the classification tracks. A track switch establishes a temporary connection between the hump tracks and a selected one of the classification tracks such that the car can roll in the classification tracks. A departure train is constituted when the requisite number of cars has been placed in a set of classification tracks. When the departure train leaves the switchyard, the set of classification tracks become available for building a new departure train.
The second type of switch mechanism is a flat switch. The principle is generally the same as a hump yard except that instead of using gravity to direct cars to selected classification tracks, a locomotive is used to push the car from the receiving tracks to the selected set of classification tracks.
In order to increase the efficiency of switching operations railway companies have developed the concept of car blocking. Under this concept, a block of cars, hence the name “blocking”, may be logically switched as a unit in a switchyard. A block is established on a basis of certain properties shared by the cars belonging to the block. For instance cars that have a common destination point on their route can be blocked together. A “block” is therefore a logical entity that helps making switching decisions. For reference it should be noted that generally, two types of blocks exist. There is the so called “yard block” and a “train block”. For clarity, the term “block” alone in the present specification encompasses either a yard block or a train block.
The principle of blocking, either yard blocking or train blocking increases the efficiency with which cars are processed at switchyards. However, it also brings constraints. Very often a train block must be assembled from cars that arrive on different incoming trains. The train block will be complete and available for departure only when all the cars that make up the train block have arrived at the switchyard. If one or more of the cars are delayed the train block cannot be completed and the entire departing train that pulls this train block may leave without the delayed cars. Such occurrence may create a cascading effect throughout entire segments of the railroad network and have significant financial repercussions for the railroad operator. Specifically, it is not uncommon for an operator to guarantee car arrival times to customers and delays incur financial penalties that may be significant.
In general switchyard operations can be classified in two categories. The first category encompasses post-switching activities, in other words activities after a car or a group of cars are switched. The key objective of the post-switching activities is the selection of the classification track in which the car or group of cars will be placed. The second category includes pre-switching activities. Those include, for example, disassembly of the arrival trains into cuts, mechanical inspection of the cuts and other suitable preparation and finally the driving of the cars making up the individual cuts to the switch.
Prior art pre-switching activities are carried on a first-in, first-out (FIFO) basis. In other words, the cars are switched in the order in which they arrive at the switchyard. This is not optimal since in many cases there may be an operational advantage to switch the cars in a sequence that is different from the sequence in which they arrive.
Against this background, it can be seen that a need exists in the industry to develop more refined processes to manage pre-switching operations in a switchyard such as to increase the efficiency with which cars are processed by the switchyard.